1. Field of the Invention
The present invention relates generally to an electrical plug, and more specifically to an electrical plug which locks the plug into an electrical outlet to prevent accidental disengagement of the plug from the outlet.
2. Description of the Related Art
Electrical power cords are used to carry electricity from electrical outlets to a multitude of electrical devices. These devices are heavily used almost everywhere in the world. Unfortunately electricity is not only useful; it is highly dangerous. The electrical energy carried by typical electrical cords is quite capable of inflicting serious injury or even death to a person who comes into direct contact with it.
Inadvertent contact with dangerous amounts of electrical energy can happen in many ways. For instance, a partially plugged electrical connector is still capable of carrying electrical energy, but fingers especially the small fingers of children, can easily reach the exposed power blades of the electrical plug. Another danger of a partially plugged electrical plug is that of intermittent power. The user of an electrical device, such as an electric saw, may turn the device on, observe no action, and assume the device is not powered. However, a slight jostling of the electrical cord providing electricity to the device may provide power to the device unbeknownst to the user. The user may then treat a powered device as though it were not powered, and serious injury may result. A third category of dangerous electrical situation is that in which a powered electrical device is causing harm and the electrical plug cannot be easily reached. In this situation, a locking electrical plug that was designed and built with safety in mind becomes a hazard itself. Thus, the Underwriters Laboratory has written specifications for the minimum force that it should take to remove an electrical plug from an outlet AND the maximum force that it should take to remove an electrical plug from an outlet.
The danger inherent in electricity is not new, nor is the concept of locking electrical plugs. Thus there exists many designs for locking electrical plugs. However, the existing designs all have drawbacks that need to be addressed. Many of the existing designs require the presence of a ground pin (e.g. Brock, U.S. Pat. No. 5,249,976, Warren, Sr. et al., U.S. Pat. No. 5,082,450, and Imhoff, U.S. Pat. No. 4,544,216). Though the use of ground pins is generally accepted as safer than the alternative, their use is hardly universal. Other locking plug designs require the use of a turning tool (e.g. Propp, U.S. Pat. No. 5,194,013 and Cohen, U.S. Pat. No. 3,345,603). Unplugging the Propp and Cohen designed plugs without their respective turning tools, which may not be handy in an emergency situation, would require forces of unsafe magnitudes. Other locking plugs are prohibitively complex for the production demands of modern commerce. In addition, many of the existing plug designs are not meant to be unplugged by merely pulling on the cord with a deliberate force within the Underwriters Laboratory maximum limit (e.g. Brock, U.S. Pat. No. 5,249,976, Murchison, U.S. Pat. No. 3,390.404, Bergwall, U.S. Pat. No. 3,676,831, Baker et al. U.S. Pat. No. 3,267,408, Hime, U.S. Pat. No. 3,187,291, and many others). Many of the designs just listed would require physically damaging the locking plug or the electrical outlet to unplug the locking plug without operating the release mechanism. Lastly, manufacturability, and thus product reliability at a reasonable cost to the consumer, is rarely addressed, especially with older locking plug designs
There exists a need for a locking electrical plug capable of remaining plugged under rigorous usage, capable of remaining plugged under the small pulling forces experienced during normal electrical device use and also the small forces provided by children, and capable of being unplugged by the application of a reasonable pulling force without the operation of a release mechanism. In addition, there exists a need for a locking electrical plug which is reliable and cost effective to both produce and purchase.